Exploration tool



Feb. 24, 1959 J. w. ANDERSON ET AL 2,375,347

' EXPLORATION TOOL Filed Dec. 28, 1954 3 Sheets-Sheet l C R Me fer 65 Q m Y INVENTORS 2 2 v 5 Jesse 14/. Anderson BY Loyc/f. El/OHS ,QTTORNEYS reb. 24, 1959 J. w. ANDERSON ET AL 2,875,347

EXPLORATION TOOL Filed D ec. 28, 1954 s Sheets-Sheet 2 I N V EN TORS Jesse I44 Anderson BY LoyaE. I/an5 ATTORNEYS Feb. 24,1959 J."W. ANDERSON ET AL EXPLORATION TOOL Filed Dec. 28, 1954 3Sheets-Sheet s IN V EN TORS Jesse l4. Ana arson By Logo 5. fvans 14 TTOIQ/VE Y5 United States Patent 'O EXPLORATION TOOL Jesse W. Anderson and Loyd E. Evans, Tulsa, Okla, assignors to The Dow Chemical Company, Midland, M1ch., a corporation of Delaware Application December 28, 1954, Serial No. 478,048

1 Claim. (Cl. 250-108) This invention relates to apparatus and methods for locating fractures in earth formations penetrated by a well bore, and particularly to apparatus for and a method of indicating the orientation of the fractures with respect to the longitudinal axis of the well bore.

In recent years a new type of oil well treatment, known as hydraulic fracturing, has been widely used to increase the recovery of oil from the earth. In hydraulic fracturing treatments sand laden materials are injected into a well bore under such a pressure that the sand laden material enters the oil producing formation through cracks or fissures produced or enlarged by the high pressure involved in the treatment. It has been theorized that the sand particles prop open the cracks or fissures after the treating pressure is removed, thus providing enlarged passageways for oil to reach the well bore.

A discussion of well treating of the above general type may be found in U. S. Patent No. 2,354,570, issued July 25, 1944, to Benckenstein.

In hydraulic fracturing, it is believed that the viscosity of, the sand carrying material is instrumental in determining if the fractures produced in the formation being treated are of the vertical or horizontal type. For example, when highly viscous fluids are used as the sand carrying material, the fluid resists entry into small naturally occurring fissures in the formation and the fluid pressure on the well bore increases somewhat uniformly (as pressure on a pipe wall builds up) until .a longitudinal (vertical) fracture occurs which is analogous to a rupture of a pipe along its seam. On the other hand, when low viscosity sand carrying fluids are used, it is believed that the fractures resulting from the treatment are predominantly of the horizontal type since the low viscosity fluid is free to enter naturally occurring horizontal cracks in the earth formation surrounding the well bore.

, However, even if the above hypotheses as to the types of fractures which generally occur under the conditions named are generally true, the well owner needs to know the specific type of fracturing which occurs in each well treated in, order to better plan supplementary fracturing treatments or, if he knows the orientation of vertical fractures, in order to modify the drilling pattern of future wells in accordance with the pattern indicated by the vertical fractures. Further knowledge of the precise distance the fractures extend along the well bore is of use in determining the depths and/ or azimuthal position at which the well will be perforated after the casing has been cemented.

Accordingly, an object of this invention is to provide an improved method of and means for locating and identifying horizontal and vertical fractures in earth formations.

, Another object of this invention is to provide an improved means for identifying vertical fractures in earth formations and determining the azimuthal orientation thereof.

In accordance with this invention, there is provided an exploration instrument, adapted to be lowered into a well bore, which contains a rotatable radiation measuring device or detector having directional pick-up characteristics. The output of the radiation measuring device is coupled to a counter at the surface through an electrical conductor in the cable by which the exploration tool is suspended. The tool contains means for indicating the azimuthal orientation of fractures which are detected by the radiation measuring device.

In practicing the invention, small radioactive beads are inserted into sand carrying fluid near the end of a formation fracturing treatment. These small beads. are then forced into the fractures under pressure, a substantial number remaining there after the fracturing treatment is completed. The well bore is then swabbed to clean out radioactive beads in the well fluid since such beads may tend to cling to the walls of the well bore. The exploration instrument is lowered into the well bore and when at the depthwhere the formation was treated, the tool is made to scan the borehole wall. The presence of fractures is indicated by the increased radiation due to the radioactive beads which were driven into the fractures. Vertical and horizontal fractures are identified by variations in radiation count rates as the borehole wall is scanned. The orientation of vertical fractures is shown by direction indicating means incorporated into the tool. I

The invention, as well as additional objects and advantages thereof will best be understood when the following detailed description is read in connection with the accompanying drawings, in which: i

Fig. 1 is a diagrammatic view of a simulated well bore containing simulated horizontal and vertical fractures and showing the exploration instrument of the invention suspended from a cable within the well bore and also showing the count rate indicator which is coupled to the cable at the surface; V

Fig. 2 is an elevational view of the exploration tool of the invention with some parts cut away to show internal structure;

Fig. 3 is a sectional view taken along the lines 3-3 of-Fig. 2;

Fig. 4 is a schematic view of self-contained photographic means for recording the azimuthal orientation of the scanning slot of the tool shown in Fig. 2; v

Fig. 5 shows diagrammatically the relative position of the photographic film of the recording means in Fig. 4 with respect to the slot in the exploration instrument shownin Fig. 2;

Fig. 6 is an elevational view, partly in section, of an e exploration tool in accordance with the invention in which the tool has motor-driven means for scanning the well bore wall;

Fig. 7 is a sectional view taken along the line 77 of Fig. 6, showing the rotation indicator contact; 7

Fig. 8 is a sectional view taken along the lines 8-8 of Fig. 6, showing the upper bearing assembly for supporting the rotating lead shield;

Fig. 9 is a sectional view, taken along the lines 9-9 of Fig. 6, showing the scanning .slot in the rotating lead shield; and

Fig. 10 is a sectional view taken along the lines 10-10 of Fig. 6, showing the coupling means between the rotating lead shield and the drive motor shaft.

, Referring to Fig. 1, there is shown a well bore 20 1 penetrating simulated earth formations 21 having a simulated horizontal fracture 22 and a simulated vertical fracture 24 extending outwardly from the well bore. The simulated vertical fracture comprises a seam diametrically disposed on opposite sides of the bore 20 which is packed with sand containing dispersed radioactive particles.

A radiation detection exploration instrument or tool 26 is suspended in the bore hole 20 by a cable 28 which passes over the sheave 30 of a derrick 32 and thence to a draw works 34. The cable 28 contains one-or more electrical conductors (not shown in Fig. 1) through which control signals, power, or data signals may be transmitted between the surface 36 and the exploration instrument 26. A cable length measuring device 38 which engages the cable 28 is provided for determining the sub-surface depth of the exploration instrument 26. A count-rate meter 40 for indicating the intensity of radioactivity along the well bore is provided at the surface 36 and is coupled to the exploration instrument through the cable 28.

The exploration instrument 26, shown completely assembled in Fig. 2, comprises an elongated tubular housing 42 (usually metal) which contains the radiation detection device 44 which may be a Geiger-Muller tube (plus its power supply and an amplifier in some cases), and well bore engaging members 46 which are utilized in rotating the part of the tool 26 which contains the radiation detection device 44.

The walls of the tubular housing 42 are of sufiicient thickness to substantially shield the radiation detection device 44 from radiations from the radioactive materials disposed along the well bore 29. The housing wall contains a longitudinal slot 48 which permits radiation emanating from earth formations which face theslot 48 to pass through the slot and impinge upon the radiation detection device 44. The longitudinal slot 48 is usually covered-with a metal sheet 50 which is used to seal the tubular housing from liquids in the well bore 20 but which does not materially impede the passage therethrough of radioactive radiation of the gamma ray-type. The sheet 50 is secured to the tubular housing 42 by the bolts 52 or other suitable means.

Referring to Figs. 2 and 3, the well bore engaging part of the tool 26 has, in addition to the well bore wall engaging elements46, a body part 54. The body part 54 is a length of pipe having one end coupled in a liquid tight manner to the tubular housing 42 and having a threaded connector 56 on the other end. The threaded connector 56 comprises the means by which the exploration tool 26 may be attached to a cable socket or other instrument containing section (not shown in Fig. 2).

An electrical conductor 58 extends through the pipe 54 and into the tubular housing 42 where it is coupled to the radiation detecting device 44. The other end of the electrical conductor 58 is secured to a button electrical contact 60 which extends from the end of the pipe 54 having the threaded connector 56. The button contact 60 is insulated from contact with the threaded connector 56 as by a bushing.

Referring to Figs. 2 and 3, the outer surface of the pipe 54 contains a groove 62 in the form of a spiral which extends completely around the pipe 54, the pitch of the spiral being such that alength of 1 foot along the longitudinal axis of the pipe 54 is required to make the complete loop around the pipe. Three bow springs or well bore wall engaging elements 46 extend radially outwardly from the pipe 54, are spaced 120 apart around the pipe 54 and have their ends attached to upper and lower slip rings 64, 66. The upper slipring 64 contains a threaded bore 68 which contains a ball bearing 70. The ball bearing 70 is held in place in the bore 68 by a screw 72, the bore 68 being so disposed that the bearing 70 rides in the spiral groove 62 on the pipe 54. An annulus or stop member 74 fits over the pipe 54 and is secured thereto at the lower end of the spiral groove 62 in order to restrict the relative movement between the slip rings 64, 66 and the stop member 74. In practice, the stop member or annulus 74 is disposed approximately half way between the ends of the pipe 54. The position of the stop member corresponds to the point on the lower part of the groove 62 which marks a complete revolution of the groove 62 around the pipe 54, assuming the groove to extend from the stop member 74 towards the threaded connector end of the pipe 54. The power source (not shown) for supplying the operating potentials to the radiation detection device 44 is disposed within the tubular housing 42 (near the end to which the pipe 54 is secured, for example). An electronic amplifier (not shown) is usually provided within the housing 42 for amplifying the output signals of the detection before they are transmitted above the surface 36. Alternatively, the power source and amplifier may be in a separate housing disposed above the well bore engaging part of the tool 26, for example, and the necessary electrical leads passed through the pipe 54 to the radiation detection device.

As mentioned previously, near the end of the formation fracturing treatment of a well, particulartcd radioactive beads or particles are injected into the fluid being pumped into the well. These radioactive beads are then forced into the fractures produced in the earth formations adjacent to the well bore.

In performing the fracture locating and identifying operation, the exploration tool is first lowered to the depth in the bore hole at which fracturing is expected to have occurred. When this is done, the lower slip ring 66 will be abutting the annulus or stop member 74. The tool 26 is then alternately raised two feet and lowered one foot to cause the tubular housing 42 to rotate, the scanning of the well bore wall being done during each lowering operation. (It is recognized that rotation of the tubular housing 42 in either direction results in scanning of the wall of the well bore 20. However, for the sake of consistency only the rotatory movement of the tubular housing 42 which results from each lowering cycle is used in graphing the radioactivity along and around the well bore 20.)

Referring to the simulated well shown in Fig. l, as the exploration instrument 26 is drawn towards the surface 36, the instrument 26 passes the simulated vertical fracture 24. As the scanning slot is rotated, strong radiation will be detected as the slot 48, detection device 44, and the fracture are in alignment. The radiation count rate, assuming constant radiation density, is a function of the area of the detector which is exposed to the radiations. As the scanning slot 48 is initially drawn past a vertical fracture, as by raising or lowering the instrument 26, only a fraction of the length of the slot 48 may be opposite the fracture, and the radiation count rate then will be smaller than when all the slot 48 is so positioned as to be opposite a vertical fracture. Similarly, as the exploration tool is drawn above or lowered below a vertical fracture, a tapering oif of the radiation count rate will be noted. Since the count rate will be high (in the case of vertical fractures) only when the slot 48 faces a fracture, the output of the radiation detection device will tend to be in pulse form. An indication of the length of the vertical fracture which lies along the well bore wall may also be obtained by examining the radiation intensity pattern.

Referring again to Fig. 1, as the exploration tool is drawn up the well bore 20, it passes the simulated horizontal fracture 22. Since the horizontal fracture 22 extends pancake-like around the well bore 20, the output of the radiation detection device 44 will be substantially constant as the scanning slot 48 is rotated. The width of the horizontal slot can also be estimated. For example, when a 3 foot long scanning slot 48 is used (assuming the detector to be at least-of similar length), an increased outputon the count rate indicator over a four foot range of vertical scanning along the bore hole 20 would indicate a horizontal fracture having a thickness along the well bore of 1 foot. (The increase in output atthe count rate indicator 40 would start as the top of the scanning slot 48 approached the bottom of the fracture 22 and would end as the bottom of the slot 48 left the top of the fracture 22.)

While the exploration instrument 26 as thus far described will indicate the presence of and differentiate'bea tween different types of fractures, additional means must be provided if the azimuthal orientation of vertical fractures are to be indicated.

One suitable means for determining the azimuthal orientation of vertical fractures is illustrated in Figs. 4 and 5. Fig. 4 shows, in diagrammatical form, photographic means for recording compass readings at predetermined intervals during the operation of the exploration tool 26. As shown, the azimuth indicating means is disposed in the upper end of the tubular housing 42. A small camera 76 has its lens focused on a translucent screen 78. A magnetic compass element 80 is disposed below the translucent screen 78 and above a light source 82. The electrical conductor 58 in the cable 28 may be used both to energize the radiation detection apparatus of the tool 26 and to operate the camera 76 and light source 82. When an azimuth indicating means of the type shown in Fig. 4 is used, both alternating and direct current are transmitted through the conductor 58 from either an A. C. source 84 or a direct current source 86 to control and energize the tool. A switch 88 at the surface is provided to enable either current source to be coupled to the cable conductor 58 to energize the tool.

The conductor 58 is connected within the tubular housing 42 to the center (movable) contact 90 of an alternating current actuated relay 92. One end 94 of the relay winding is coupled to the center relay contact through a condenser 96'and the other end 98 of the relay winding is grounded to the housing through which the ground return to the surface is made through the steel conduc-v tor (not shown) of the cable 28. The movable center contact 90 of the relay is loaded by a spring 100 to keep the center contact 90 connected to a D. C. contact 102 unless the relay winding 104 is energized by alternating current. The camera 76 is of the roll film type in which the tripping of the shutter (not shown) advances the film for the next exposure. Amovie camera having a single frame exposure control is typical 'of such a camera. The exposure control of the camera 76 is actuated by a solenoid switch 106 in the D. C. circuit of the exploration tool 26. Likewise, the light source 82 is included in the D. C. circuit. As shown in Fig. 4, the light source 82 and the solenoid switch for operating the camera 76 are connected in series. However, parallel wiring for the solenoid switch 106 and the light source 82 may be used.

When A. C. is applied to the conductor 58, the winding 104 is energized and the A. C. is passed through the contact 108 to the radiation detection section of the tool 26.

Fig. 5 illustrates diagrammatically the relationship between the film of the camera 76 and the longitudinal slot 48 in the tubular housing 42. The arrow 110 indicates the orientation of the compass element 80 as recorded on the film 112. Since the slot 48 has fixed orientation with respect to the film, the angle between the compass element 80 and the slot 48 is an indication of the azimuthal orientation of the slot 48.

In operation, using the photographic means of Fig. 4, alternating current is applied through the cable 28 (and the A. C. contact 108 of the relay 92) to the rotatable part of the exploration tool 26. The tool 26 is rotated graphed by the camera 76. The depth at which each camera exposure is made is recorded at the surface 36 and the orientation of the slot 48 as shown on the film is later correlated with a graph or other means showing radioactivity intensity along the well bore.

. The above described means for determining the orientation of vertical fractures in earth formations is well adapted for use with cables 28 having a single insulated electrical conductor incorporated therein. If multi-conductor cables were used, the wiring circuitry for controlling and energizing the exploration tool would be considerably different.

An alternative form of exploration tool indicated generally by the numeral 114 is shown in Figs. 6 through 10. Basically the exploration tool 114 comprises a hermetically sealed tubular housing 116 (corresponding to the hermetically sealed housing 42 in the tool 26) which contains a radiation detection device 118. This is surrounded by a rotatable metallic shield 120 which is driven (rotated) by a motor 122 which is contained within the housing 116.

The housing 116 is capped at its lower end by a'plug 124 which serves as a base on which the motor and other parts are mounted. The plug 124 is retained within the housing by set screws 126. The upper end of the tubular housing 116 is enclosed by a cap 128 which engages the threaded upper peripheral surface 130 of the housing. The upper part of the outer peripheral surface 132 of the cap 128 is threaded to permit the attachment thereto of a cable socket 134 or other section of the exploration tool assembly. A tubular support 136 is secured to the top of the cap 128 and extends downwardly into the housing 116.

A hollow cylindrical member 138 is mounted below the lower end of the tubular support through a coupling 140 connecting the cylindrical member 138 to the tubular support 136. The cylindrical member 138 contains, near its lower end, a radiation detection means in the form of scintillation crystals (indicated by the dotted lines 118), the output of which is coupled (through leads not shown) to a male terminal socket 142 which extends from the top of the cap. In practice, the signal output of the scintillation crystals 118 (or other radiation detection device) is often amplified by a photomultiplier tube (not shown) which is contained within the cylindrical member 138. The cylindrical member 138 is mounted coaxially with respect to the tubular housing 116.

The cylindrical member 138 is surrounded over most of its length by a cup-shaped shield 120, which may be made of lead. The rim end 144 of the cup-shaped shield 120 is of reduced diameter. A split ended hollow shaft 146, shown also in Fig. 10, extends from the base end of the cup-shaped shield. The shaft 146 is made of steel, for example, which is embedded in the lead of the shield 120.

Referring especially to Figs. 6 and 9, an aperture 148 is provided in the wall of the shield 120 opposite to the location of the scintillation crystals 118 or other radiation detection means. The size of the aperture 148 varies with the type and sensitivity of the radiation detection means. Generally speaking, however, a small aperture (which is large enough to pass sufiicient radiation to get a usable output signal from the radiation detection means) provides better definition of the fractures by virtue of its tendency to collimate the beam of radioactive rays.

The shield 120 is supported on a thrust bearing 150 which is carried by an apertured bearing plate 152. The bearing plate 152, which contains a counter bore or recess 154 in which the thrust bearing 150 is held, is supported within the tubular housing 116 by four bolts 156 which threadedly engage the bottom plug 124 of p the tubular housing 116. The drive motor 122, which is electrically driven but which could be a spring actu ted motor, for example, is mounted on the end plug ll with its drive shaft 158 extending through the aperture 160 in the bearing plate 152 and engaging the split ended shaft 146 extending from the base of the shield 120. A transverse pin 162 extending through the end of the drive shaft 158 and through the slot opening in the slotted split shaft 146 is utilized to transfer power 7 from the drive shaft to the split shaft extending downwardly from the shield 120.

One electrical lead 164 of the drive motor is grounded t the metal housing (at 166) while the other lead 168 passes upwardly through a small aperture 170 in the bearing plate 152 and between the shield 120 and the tubular housing 116, through an opening 172 in the tubular support 136 and is connected to one of the contact pins 174 of the terminal socket 142 on the top cap 128.

Referring especially to Figs. 6 and 8, the upper end 144 of the shield is supported laterally by a needle bearing assembly 176 which fits between the rim part 178 i of the shield 120 and the interior surface 180 of the tubular housing 116. The outer race 182 of the bearing assembly contains an aperture 184 through which the lead 168 passes. The inner race 186 fits snugly against the rim part 178 of the shield 120 and is separated from the outer race 182 by a plurality of needle bearings 188. A rotation indicating means 190 is provided on the exploration tool 114 shown in Fig. 6. As shown in Figs. 6 and 7, the rotation indicating means comprises an electrical contact pin 192 which extends from the coupling 140 and engages a flexible wiper contact 194 which is affixed to the upper or rim end 144 of the shield 120. The contact pin 192 is so coupled to the signal lead not shown from the radiation detection means that as the wiper-contact 194 passes the pin contact 192, the signal output from the radiation detection means 118 is momentarily grounded. This lack of signal output (noise in the radiation detection system provides some output even if no radiation is detected) gives an indication that the shield 120 is being rotated.

Azimuthal direction indicating means of the type heretofore described or of other suitable types may be utilized as a part of an exploration tool incorporating a scanning device of the type shown in Figs. 6 through 10. The electrical circuitry of the direction indicating means is a matter of choice, depending on the number of conductors in the suspending cable and on the type of device used.

In operation, a scanning tool 114 of the type shown in Figs. 6 through is lowered into the well bore. A cable length measuring device 38 (as in Fig. 1) at the surface 36 indicates the depth of the-tool 114 in the well bore 20. The tool 114 is slowly passed through the areas suspected of containing fractures into which radioactive tracer elements have been driven. The shield is rotated, scanning the bore hole wall for radiations emanating therefrom. The rate of rotation of the shield 120 should be correlated with the rate of descent or rise, of the tool 114 along the well bore 20 to provide an adequate indication of a horizontal fracture as the tool is drawn up or down the bore hole. That is, to show a complete horizontal fracture, the shield should rotate at least approximately one revolution during the time required to draw the scanning aperture completely past a horizontal fracture.

A horizontal fracture is indicated by a long period (time required for a revolution of the shield, for example) of detected radiation at a single depth while a vertical fracture is indiacted by short peaks of detected radiation at a plurality of depths in the well bore.

The azimuth indicating means, if incorporated as part of the exploration tool, may be used to determine the orientation of vertical fractures.

In the case of either type of fracture, the comparative intensity of radiation emanating from the fracture is a general indication of the magnitude of the fracture.

Thus, the present invention provides a convenient and accurate means for determining the location, orientation, and magnitude of fractures in earth formations.

We claim:

An exploration tool adapted to be suspended in a bore hole which penetrates an earth formation comprising a hermetically sealed housing containing a Geiger-Muller tube, tubular shield means enclosing the said tube and containing a longitudinal slot-like aperture disposed opposite to said tube, a thin, fluid impervious covering for said aperture, and means including well bore wall engaging elements for laterally rotating said slot-like aperture for at least one complete revolution whereby the aperture scans the wall of the bore hole.

References Cited in the file of this patent UNITED STATES PATENTS 

